Engine/Transmission (1994 - 1998) Taking Spells Of Running Rough

[CEdwards]

For almost a year my truck has been taking spells of running rough. at first it was hardly noticeable. It only happened a couple of times going down the interstate(just a slight change in the way it sounded and slight cutting out just momentarily). I dismissed it as bad fuel and needed a filter change. since then it has increased more and more. now it's not reliable enough to drive it out of town. It could just be a minor miss or it could die completely or any where in between. It could go a month or a day and run just fine. If its a bad spell going down the highway it will rev like the throttle is stuck and then die. It always starts back up immediately even if i have to give it a little pedal until it can idle on its own. when it is cutting out there is a slight ticking noise under the hood. It is usually brought on under load like running out of fuel, but once it cuts out once it will only get worse the rest of the day even with no load. after it sits all night it is fine the next day. I have read similar stories on here and have researched it. I've changed the fuel filter and drained it to see if theres water when it cuts out and there is none. I have changed the prefilter screen. I've looked at all the fuel lines, but haven't replaced any cause they look fine to me. I put a new tank on 6 months ago so i know the problem isn't there it was acting up before the tank. I don't have any fuel leaks but could have an air leak that i don't know about. have also replaced fuel solenoid with cable so thats not it. My thoughts now are to mount a fuel pressure gauge so i can monitor the pressure during a spell to see whats going on. If it has pressure during the spell then it must be the injector (right?). does it sound like air? Any ideas or similar stories would be appreciated. thanks.

 

[CEdwards]

forgot to mention I haven't checked the by-pass spring on the injector. Was just gonna start throwing parts at it but a new one was priced at $160 at the dealer. Doesn't seam like that would be the problem since it happens so randomly instead of a constant problem.

 

[ABorchard]

The overflow (bypass) valve is always the first part to throw at it, one of the few parts that wears out at less than a 100k on a 12 valve.

Cheapest source by far

Precision Diesel Injection and Turbo Inc.

888-734-7349

$35 + $7 shipping and handling



Forgot to mention, I've run into a few with the symptoms you describe, new OF valve, cleaning heater screen or changing main filter has cured it.

 

[CEdwards]

I ordered the overflow from precision diesel and will put it on when it gets here. It's amazing how much price difference there is. dealer was $165 and perf. diesel was $35. It took a mild spell today and i pulled in to top off the tank. It was idling and barely running when i started to fill it up, but ran perfect as soon as i pulled out. I think it was just coincedence cause it has ran fine when it was a lot lower on fuel than that, but that might be the next thing i look into after the overflow valve. Maybe just at certain times I am getting an air leak.

 

[bmoeller]

The rubber lines can let air in the system, without leaking fuel.



Get the overflow valve on there, then check the fuel pressure. Could be the lift pump also, getting weak.



At your miles, I doubt it would be a problem yet, but, it could be a fuel injection pump, at the worst. Had a tractor that was running like that. It was the f. i. p. , in that case.

 

[ABorchard]

It was idling and barely running when i started to fill it up, but ran perfect as soon as i pulled out.

My feeling is that the spring in the OF gets weaker

with age and heat causes it to lose even more springiness. Lower fuel tank level results in hotter fuel since the return fuel doesn't have as large of a reservoir cool in. Before I replaced my OF valve the problem would never crop up unless my fuel level was below half a tank.

I also had the same kind of fuel station experience, limped into a station at barely an idle, after just a couple minutes of filling the truck was running fine again.

 

[CEdwards]

Here we go again. My truck has been running fine for the last month or so since I put a new overflow valve on so I figured that must have been it problem solved. until today. It seems that in order to take one of these spells it has to be 20 gallons low and you have to be under load or driving 80mph to get it to start running rough. again it feels like running out of fuel. when i let off accelerator rpms stay up for a 4 or 5 seconds then it will die. can start it back up by giving it a little pedal when i crank it and hurry up and put it into gear. It died and i coasted into gas station, fueled up and ran great leaving there. couldn't get it to run rough for anything.



alright heres my question. obviously i need a fuel pressure gauge to see whats going on, but if I have low fuel pressure how will i know if its a problem in the tank or a weak lift pump. given the fact that when the tank is low it acts up im starting to think i should just pull the tank and check it out. any ideas or advice would be appreciated as i need to get it fixed soon so i can take it on some out of town trips this summer. thanks.

 

[Joe G.]

Low fuel pressure will tell you if you are getting fuel to the injector pump correctly. If the pressure is low then you have a problem between the fuel tank and the injector pump. Fuel hoses can look fine and leak air like crazy. If you have not replaced them you eventually will have to, so it's a good idea to get a new set from Larryb anyway. I really don't think it is the lift pump or it would be a constant problem. You should check the fuel heater for an air leak. It's easy to remove and the pre-filter will mount right up to the bracket without the fuel heater being there so it's really easy to check. If it's leaking air the fuel heater will still look fine. Remove it and screw the pre-filter back on. See if that helps.



You also could have a leaking fitting somewhere.

 

[CarlJensen]

On an older model the prob is not normally the fuel pressure but the OF valve, a leak in a fuel line, plugged heater screen or filter or a leaking pickup in the tank. The pickup in the tank can leak air into the line or some have a pre pickup screen on them that gets clogged. When you fill the tank increased fuel weight pushes more fuel through to make it run better again. Do the easy first, check filter and fuel bowl/screen at bottom of fuel heater. While the heater is off check it for cracks around the wire connection point. Check rubber fuel lines for checking or pinholes, they can leak air in and not leak fuel out.

 

[TWafer]

Sounds similar to a problem I had a few years ago. It took well over a year to diagnose but finally traced it to a suction leak inside the fuel tank. The line from the top of the tank to the bottom had a tiny air leak in it. It never bothered on a cold day but on a warm day it sucked! :-laf (pun intended). Apparently the plastic line would contract enough on a cold day to stop the leak. I finally realized the problem never appeared if the tank was completely full since the leak then would be in the fuel. I fixed it by replacing the line with a one-piece stainless tube and never had the problem since.

Tim

 

[CEdwards]

I have already replaced overflow and prefilter screen. If i'm understanding joe g. right i think i can take the filter bowl back off, take heater off, put it back together and leave the heater off. I think i read somewhere on one of his posts that he did this. correct me if i'm wrong. I've also changed fuel filter 3 times. also i was able to make it act up today by driving 80 on the highway with a full tank and yes it was warmer outside today. so next i will:



#1 take off fuel heater and run without it if thats possible



#2 go ahead and replace all rubber fuel lines. (whats best to use? I think when i was searching i ran across a post on how to do it and is there a certain hose or kit to order?)



#3 if that doesn't solve it then i will pull tank off



anything else? i appreciate all the good advice. I am learning more and more everyday thanks to all the good people of the tdr.

 

[ABorchard]

Rather than throwing parts at it I'd go for a fuel pressure gauge first. You might have to consider the new o/f valve is already bad. If you bought it from Marty I'm certain he'll send you a new one.



When mine was having this same problem I added a new overflow valve and fp gauge at the same time. No low pressure and no problems for several years now . Believe me after having this problem for a couple years, living with it by keeping the fuel level up, I knew exactly how to make the problem appear and it hasn't.



Problem with the sucking air advice you recieved thus far is that an air leak will almost always cause hard starting if the truck sits overnight.



Another thing I've heard of that can cause the same sort of problem is a weak shutdown solenoid that doesn't hold all the way open when it gets hot. Guess you'll have to catch it in the act but this couldn't be connected with lower fuel levels.

 

[CEdwards]

i've already replaced solenoid with pull cable and checked it to make sure it is up all the way and I never have any problems starting. always starts first crank no matter what so it doesn't sound like air leak, but i will replace them since they're old so it won't leave me on the side of the road someday. the only way to make it act up seems to be when its warm outside and your driving 80 or pulling heavy load. acted up today with full tank but was warmer outside so before when it was low it was probably acting up when the fuel got warmer but now its warm enough outside. it would almost have to be a restriction by the way it acts im running out of fuel. will do a search on here about putting on fuel gauge. would it be alright to just put it in the fitting on top the filter or do i need to drill and tap banjo fitting like i've seen on here.

 

[Joe G.]

I've been running without a fuel heater for some time. No problems at all. A bad fuel heater looks fine. The heating element inside burns apart at one of the contacts. That heats up the black plastic so there is an air leak around the electrical plug. There are no visable cracks in mine. You might try to put some grease around the electrical plug and put it back it. That may stop the leak if it is not too bad. If it was a bad leak you would have hard starting after it sat for a while. You would also see low fuel pressure in that case. When you are running it hard with a small leak you may get enough air sucked in to affect it. No way to tell without some tests that affect the problem.



There are pictures of my bad fuel heater in my Reader's Rigs gallery.

 

[CEdwards]

Finally got the fuel pressure gauge installed at the banjo bolt. 30psi at idle. Only got it to go as low as 24psi accelerating hard up hill. couldn't get it any lower for anything. I tried everything to get it to act up but it wouldn't do it today. when it finally does i will post my results. thanks.

 

[ABorchard]

Sure fire way to make it show up is a low fuel level and a hill with no place to pull over.

 

[CEdwards]

Sorry to keep dragging this up and asking amatuer questions but i thought I might run my latest problem by some experts and see if you have any ideas.



this is what I've done so far:

1)new overflow valve

2)valve adjustment

3)new filter screen and removed fuel heater

4)new fuel filter

5)solenoid replaced with pull knob

6)fuel gauge in cab



current status:

will sometimes cut out or try to die on occasion, especially if hot outside or driving fast or low fuel but doesn't have to be all these, just one or 2 of these situations.



yesterday when i first started it it was trying to idle too high all day. would have to get out pop the hood and wiggle throttle to get it to slow down.



today when i first started it it would idle too low and keep dieng all day.



fuel pressure 25 to 30 at idle no matter how bad or good its running

can get as low as maybe 17 at times going down road even if its taking a spell it still has good fuel pressure.



I tried to research the idle problem but i'm a little confused. The throttle cable seems to be free. The linkage arm seems to be a little stiff. the rod that goes towards the back of the engine. Is that going to the governor? Is this problem connected to the other problem? does the tps or anything else have anything to do with this. It doesn't feel like the bind is in the linkage itself but its hard to push the rod back. Any help please? If it gets any worse i'll be walking soon. also i'm going to do a search on the rubber fuel line components and figure out what I need there to eliminate that possibility. Thanks for all your help i'm learning as i work through this problem.

 

[TWafer]

I would still check for a leak in the line inside the fuel tank. Most of your symptoms I experienced when I had that problem. A hot day and WOT would almost always bring it on unless the tank was chuck full to the top. It’s a plastic line with lousy click couplings. A warm day made them expand enough to leak.

Tim

 

[CEdwards]

I think I will do that this weekend. Is there any replacement parts I need to get first?

 

[CEdwards]

I replaced my fuel line from the tank to the pre filter and from pre filter to pump. Didn't have time or what I needed to replace the pickup line in the tank so I can't rule that out yet. Took it on the highway on a hot day drove it 85 for 2 miles and it started cutting out again. I'm going to run my suction line into a jug and test it again when I get a chance this week. If it still cuts out then I know the problem is not in the tank or fuel line. also, like I posted earlier my idle is erratic. It fluctuates up and down all the time now so I don't know whats going on there. There's really nothing else left to replace in the fuel system from tank to injector so are there any other ideas that could cause this? Is this any way related to my idle problem?